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TPS54620: Cannot set Vout under 6 volts

Abel Mendes
Prodigy 10 points
Other Parts Discussed in Thread: TPS54620

Mates,

I'm getting in trouble with TPS54620, because it's getting impossible to regulate the Vout under 6 volts.

I followed the schematic of figure 34 from the datasheet, with the required changes to meet the next requirements: Vin=15V; 2V<Vout<15V; Iout=4A.

But, no matter what is the Vsense voltage divider, the minimum achieved output is shown in the next figure:

 

The check points are depicted in the next figure.

I am using a 10uH inductor with 0.02Ohm. Resolving the equation 29 (of datasheet), the minimum Vout would be below 1V.

 

What can I do to get able to regulate the Vout from the entire range [1V..15V]?

 

Regards,

Abel

 

  • 0
    TI__Guru**** 150820 points

    The TPS54620 can regulate to as low as 0.8V.  What resistor values have you installed for R5 and R6?  Are you doing this testing on the EVM or is this your own board?

    Your CH3 waveform doesn't look right.  The mean value is 8.45V, while it should be regulating to 0.8V.  Please make sure that CH3 is really looking at pin 7 of the IC.  Also, do you have a screenshot of what Vout is doing during this time?

  • 0 in reply to Chris Glaser
    TI__Guru**** 191445 points

    Yes, if teh circuit is properly built, the resistor divider from Vout to V_SNS to ground (R5 and R6 in this example) is all that is required to set the output voltage.  Pin 7 should always be .8 V.  With R5 and R6 as shown, the output should be 3.3 V.